MAMMARY TUMORIGENESIS IN THE RAT FOLLOWING PRENATAL EXPOSURE TO DIETHYLSTILBESTROL AND POSTNATAL TREATMENT WITH 7,12-DIMETHYLBENZ[A]ANTHRACENE

Pregnant rats were injected with vehicle or 1.2 pg diethylstilbestrol (DES) during wk 2 or 3 of gestation; their female offspring (-50 d old) were fed 7,12-dimethyl- benz[a]anthracene (DMBA). The survivors (27 per group) were sacrificed 30 wk later. The three groups did not differ in the number of tumor-bearing animats; however, significantly more palpable mammary tumors arose in both DES-exposed groups than in controls. When DES was given during the second trimester, palpable tumors appeared earlier than in the other two groups. Thus, transplacental exposure to DES potentiated the action of a known carcinogen (DMBA) on rat mammary tissue. These results raise the possibility that, for young women, DES exposure in utero may have affected tissues other than the vagina. Further investigation is warranted, with special emphasis on the effects of DES on mammary and other estrogen-sensitive tissues. © 1979 Taylor & Francis Group, LLC.